Field of the Disclosure
The present disclosure relates to an image forming apparatus such as a laser printer, a copying machine, and a facsimile.
Description of the Related Art
Japanese Patent Application Laid-Open No. 2012-137743 discusses a conventional approach for adjusting a potential of a non-image portion (area to which toner is not adhered) of a photosensitive drum to further improve the image quality of an electrophotographic image forming apparatus. Specifically, an image portion (area to which toner is adhered) of the photosensitive drum is irradiated with light that is emitted in a first light emission amount for setting a potential for adhering toner. The non-image portion of the photosensitive drum is irradiated with light that is emitted in a second light emission amount for setting a potential for not adhering toner. The second light emission amount is smaller than the first light emission amount. To stabilize the first and second light emission amounts, auto power control (APC) for adjusting the two levels of light emission amounts, i.e., the first light emission amount and the second light emission amount, is discussed to be performed.
APC is usually performed in a period between when one line of a normal image is scanned over the photosensitive drum in a main scanning direction and when the next line is scanned. If laser light is emitted for APC, stray light may occur. As illustrated in FIG. 12, the laser emission therefore can be controlled to stop between after the two levels of APC on the first and second light emission amounts are performed and before light emission for forming a normal image is performed.
Laser elements have a characteristic called droop in which the amount of emitted light varies with a change in element temperature. As illustrated in FIG. 12, if the laser emission is stopped to prevent stray light between the end timing (t1) of the APC on the second light emission amount and the start timing (t2) of weak emission of the second light emission amount for the non-image portion, the temperature of the laser element drops. As a result, droop occurs at the start timing (t2) of the weak emission of the second light emission amount for the non-image portion, and the amount of emitted light becomes higher than desired. The rate or effect of change in the amount of emitted light due to droop increases as the amount of emitted light decreases. Under the effect of the droop, the photosensitive drum is exposed to a greater amount of emitted light than the desired second light emission amount. The drum potential can thus be lower than a desired value, in which case an image defect such as fogging can occur.